Glaucoma

What is glaucoma?

Glaucoma is a disease in which the internal pressure of the eye (the Intraocular Pressure) rises gradually or suddenly, resulting in damage to the optic nerve. The optic nerve is a vital structure for vision, as it transmits image signals from the nerve fibre layer at the back of the eye (the Retina) to the visual centre in the brain, much like an electrical cable. When the intraocular pressure around it is too high, the optic nerve begins to lose its fibres, leading to the gradual loss of vision.

What causes glaucoma?

The eyeball is a closed system full of fluid (called Aqueous humor). In the normal eye, this fluid is produced at a rate that is equal to the rate at which it is drained out of the eye, so that the pressure is maintained at a stable level. In glaucoma, there is a disturbance of this equilibrium, usually due to impaired drainage of the fluid from the eye through the trabecular meshwork in the angle of the eye. This reduced drainage results in increasing pressure in the eye, and damage to the optic nerve.

Are there different types of glaucoma?

There are different types of glaucoma.

1.Open-angle glaucoma

The commonest type of glaucoma is primary open-angle glaucoma. This type of glaucoma is often “silent” in its early stages, with no detectable symptoms (no pain or noticeable visual loss). This type of glaucoma typically is more common with increasing age, and particularly in those with a family history of glaucoma. It is often detected incidentally on a routine check with the optometrist or ophthalmologist.

2.Normal-tension glaucoma

This is a sub-type of open-angle glaucoma, whereby the measured eye pressure is within the normal range (10-21mm Hg) but progressive damage to the optic nerve still occurs. This is why the intraocular pressure measurement is not the only guide as to whether a patient has glaucoma. In fact, the intraocular pressure can fluctuate in ever patient from hour-to-hour during the day. Diurnal pressure or 24-hour pressure monitoring is a more accurate, but impractical way of measuring a patient’s true pressure. The appearance and health of the optic nerve, for a given pressure in any patient, is the more important indicator of whether a patient has glaucoma.

3.Closed-angle glaucoma

This type of glaucoma is much rarer, but potentially more damaging than open-angle glaucoma. In this glaucoma, there is a detectable physical blockage of the drainage angle of the eye, which can result in a quick fluid build-up in the eye and a rapid rise in the pressure.

Acute angle-closure glaucoma (AACG) is an emergency that can lead to rapid blindness if not detected and treated appropriately. In AACG, the pressure may suddenly rise to levels in the 60-80mmHg range, leading to severe eye pain, blurry vision, haloes around lights, headache, nausea and vomiting. These attacks often occur in the middle of the night, when the iris of the eye dilates and contributes to further narrowing of the drainage angle of the eye.

Chronic angle-closure glaucoma is more gradual, but can be more resistant to treatment than chronic open-angle glaucoma.

4.Secondary glaucoma

This glaucoma results from another eye disease. These include previous eye trauma, certain medications (particularly long-term steroids), and specific eye conditions like pseudo-exfoliation or pigment dispersion syndromes. These will be detected by the ophthalmologist.

5.Congential glaucoma

This is a very rare glaucoma that develops in infants and young children, and often inherited. It is a difficult condition to treat, and often leads to blindness if not detected and managed early.

What are the risk factors for glaucoma?

1.Open-angle glaucoma

Increasing age (particularly >40yo)
Family history, especially direct family (parents, siblings)
High myopia (short-sightedness)
Ethnicity (African-Caribbean or Hispanic)
Diabetics
History of migraine
Cardiovascular disease and hypertension

What are the symptoms of glaucoma?

1.Open angle glaucoma

This is often asymptomatic and silent in the early stages. There is never any pain in this glaucoma, just progressive visual loss. If glaucoma is untreated, the optic nerve loses more fibres over time, with the peripheral vision affected first, and gradually moving towards the centre of the vision. Patient with very advanced glaucoma have only a small central island of vision remaining (“tunnel vision”), and in the final stages even this is lost, leading to complete blindness.

Chronic angle closure manifests like open angle glaucoma, with gradual vision loss but no pain.

How is glaucoma diagnosed?

Multiple clinical parameters are carefully and simultaneously assessed in the diagnosis of glaucoma. These include:

Intraocular pressure measurements (often over a period of time)
Optic nerve appearance
Visual field testing
Corneal thickness measurements
State of the drainage angle (open, narrow or closed)

Clinical assessment of the optic nerve, in particular, is greatly enhanced with the use of advanced technology such as OCT scans, which can detect optic nerve changes well before the naked eye can.

What is the treatment for glaucoma?

Like high blood pressure, there is no cure as such for glaucoma. Treatment simply aims to lower the eye pressure to reduce the risk of progressive visual loss from sustained high pressure. All current treatments lower the eye pressure either by increasing the drainage of fluid out of the eye, or reducing the production of fluid into the eye.

1. Eye drops (Topical therapy). In the vast majority of patients, topical therapy with eye drops is enough to control glaucoma. There are various classes of glaucoma drops, which work in different ways. Most patients only need one type of eye drop to control their glaucoma, but some will require 2 or 3 classes of drops to adequately control their pressure. The eye drops are generally safe, easy to use, and well-tolerated in most patients.Side-effects can occur, and the ophthalmologist will discuss the specific side-effects of each particular drop before commencing treatment. Once on eye drops, they are generally required for the rest of the patient’s life.

2. Eye laser. There are 2 type of laser used to treat glaucoma:

a) SLT (Selective Laser Trabeculoplasty). This is generally considered a secondary therapy for open-angle glaucoma, where eye drops alone have not been successful in controlling eye pressure. After SLT, some patients may no longer require eye drops, whilst some will still require drops but less than before. SLT aims to increase the fluid drainage from the eye, by lasering the trabecular meshwork in the angle of the eye. It is performed in the clinic, and is considered a safe and well-tolerated procedure. It may require more than one session to achieve adequate pressure control.

b) YAG laser PI (peripheral iridotomy). This is used to treat closed-angle or narrow-angle glaucoma. It creates extra drainage ports in the iris of the eye, to allow easier flow of aqueous humor within the eye. It is used in both the acute and chronic forms of closed angle glaucoma. It is performed in the clinic, and is also a safe and well-tolerated procedure.

3. Eye surgery. This is rarely required these days in the management of glaucoma, but will be used if topical therapy or laser therapy fails. This surgery aims to create filtration ports for the drainage of fluid of the eye, either through a flap in the patients outer eye tissue (trabeculectomy) or through a drainage tube that passes from the inside to the outside of the eye (tube-filtration surgery).

Why is monitoring required for glaucoma?

When patients develop glaucoma, they will require long-term monitoring to ensure that their treatments stay efficient over their lifetime. Generally, annual checks are all that is required, if the glaucoma is well-controlled. These check-ups are usually performed by an ophthalmologist.

At each check-up visit, all of the clinical parameters (eye pressure, optic nerve appearance, visual fields) are assessed, to ensure that there has been no change to suggest progression of vision loss despite therapy. If there is, then the therapy is increased, either with more eye drops, or the consideration of laser or surgery.

As vision lost cannot be restored, prevention of vision loss is the key. Early detection of change or progression is very important in the long-term management of glaucoma.